<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Bootstrap 实例 - 下拉菜单（Dropdowns）</title>
    <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css">
    <script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>
    <script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
</head>
<body>

<div class="dropdown">
    <button type="button" class="btn dropdown-toggle" id="dropdownMenu1"
            data-toggle="dropdown">
        主题
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">Java</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据挖掘</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据通信/网络</a>
        </li>
        <li role="presentation" class="divider"></li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">分离的链接</a>
        </li>
    </ul>
</div>

<hr>
<div class="dropdown">
    <button type="button" class="btn dropdown-toggle" id="dropdownMenu1" data-toggle="dropdown">主题
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu pull-right" role="menu" aria-labelledby="dropdownMenu1">
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">Java</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据挖掘</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据通信/网络</a>
        </li>
        <li role="presentation" class="divider"></li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">分离的链接</a>
        </li>
    </ul>
</div>

<hr>
<div class="dropdown">
    <button type="button" class="btn dropdown-toggle" id="dropdownMenu1" data-toggle="dropdown">主题
        <span class="caret"></span>
    </button>
    <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
        <li role="presentation" class="dropdown-header">下拉菜单标题</li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">Java</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据挖掘</a>
        </li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">数据通信/网络</a>
        </li>
        <li role="presentation" class="divider"></li>
        <li role="presentation" class="dropdown-header">下拉菜单标题</li>
        <li role="presentation">
            <a role="menuitem" tabindex="-1" href="#">分离的链接</a>
        </li>
    </ul>
</div>
</body>
</html>